The present invention relates to bearings, and more particularly to a method of determining the contact angle of a ball bearing.
U.S. Pat. No. 5,423,218-A discloses a method for measuring the contact angle based on the detection of radial vibrations, by means of a pickup sensor applied on the outer ring of the bearing. The inner ring of the bearing is rotated while the outer ring is held stationary and subjected to an axial load. The signal detected by the pickup is transmitted to a frequency converter through an amplifier. The frequency converter determines, by calculation, the frequency of rotation of the inner ring and the frequency of the number of passes of the balls, and from the computation of these frequencies, it calculates the contact angle.
According to a conventional method, described in Japanese utility model JP-52 143 955-U, the contact angle is arrived at by detecting two parameters: the rotation of the inner ring and the rotation of the ball retaining cage (which corresponds to the revolution of the balls about the central axis of rotation of the bearing). A screen with opaque sectors is fixed on the cage and the outer ring is held stationary. By making the inner ring rotate, the opaque sectors of the screen intercept the light beam of a photocell, providing for the detection of the rotation of the cage.
The abovementioned conventional method is not very precise and has limits of a practical nature. Specifically, for bearings of very small dimensions in which the space between the inner diameter of the outer ring and the outer diameter of the inner ring is minimal, applying a support on the cage for a screen with opaque sectors in order to detect the rotation of the cage is problematic. The fitting of the screen is made more difficult if the rings of the bearing are flanged, or if the bearing is already assembled in a defined apparatus/machine. The play existing between the balls and the seats of the cage in which the balls are housed does not allow to determine the angle of revolution of the balls accurately. Furthermore, the screen fitted to the cage increases the inertial mass of the same cage; i.e. it can cause the balls to slide along the raceways and negatively affect the precision of the measurement of the contact angle.